lavc: fix avcodec_find_best_pix_fmt() when there's more than 64 pixel formats

This fixed the problem where if there's more than 64 pixel formats
defined avcodec_find_best_pix_fmt() returns the wrong pixel format.
Signed-off-by: Matthew Einhorn <moiein2000@gmail.com>
Signed-off-by: Stefano Sabatini <stefano.sabatini-lala@poste.it>

libavcodec/avcodec.h

@@ -3499,6 +3499,8 @@ int avcodec_get_pix_fmt_loss(enum PixelFormat dst_pix_fmt, enum PixelFormat src_
  * The pixel formats from which it chooses one, are determined by the
  * pix_fmt_mask parameter.
  *
+ * Note, only the first 64 pixel formats will fit in pix_fmt_mask.
+ *
  * @code
  * src_pix_fmt = PIX_FMT_YUV420P;
  * pix_fmt_mask = (1 << PIX_FMT_YUV422P) || (1 << PIX_FMT_RGB24);

libavcodec/imgconvert.c

@@ -439,7 +439,7 @@ static enum PixelFormat avcodec_find_best_pix_fmt1(int64_t pix_fmt_mask,
     /* find exact color match with smallest size */
     dst_pix_fmt = PIX_FMT_NONE;
     min_dist = 0x7fffffff;
-    for(i = 0;i < PIX_FMT_NB; i++) {
+    for (i = 0; i < FFMIN(PIX_FMT_NB, 64); i++) {
         if (pix_fmt_mask & (1ULL << i)) {
             loss = avcodec_get_pix_fmt_loss(i, src_pix_fmt, has_alpha) & loss_mask;
             if (loss == 0) {